This proposal to investigate some aspects of iodine and thyroid hormone metabolism focuses upon (1) characterization of a thyroidal electron-carrier system mediating the NADPH-dependent deiodination of iodotyrosine, (2) purification and characterization of iodothyronine 5'deiodinase from kidney, (3) the role of calcium in thyroid hormone action at the cellular level, (4) the effects of iodine on thyroidal adenylate cyclase, and (5) identification and characterization of cell surface pyridine nucleotide oxidases in the thyroid with particular reference to their role in H2O2 production. With regard to (1), thyroidal ferredoxin and its NADPH-dependent reductase will be purified from thyroid particulate preparations and the structural and functional relationship of ferredoxin-reductase to flavoprotein iodotyrosine deiodinase will be studied. Goal (2) will be approached by purification of renal iodothyronine 5'-deiodinase from detergent solubilized membrane preparations with investigation of a possible phospholipid requirement, and characterization with respect to iodothyronine substrate specificity and the role of enzyme and tissue thiols in the enzyme catalyzed reaction. Goal (3) will examine the effects of altered thyroid states on the molecular forms and states of activation of calmodulins from various tissues. Effects of hyper- and hypo-thyroidism on enzymes regulated by calmodulin - especially Ca ions plus Mg ion-ATPase and cyclic nucleotide phosphodiesterase - as well as on kinetics of Ca ion transport in adipocytes and subcellular organelles will be investigated. Goal (4) will assess the possible generation of an "active oxygen" species (O2 ion, singlet oxygen, H2O2) during thyroid oxidation of iodide and other halides and its role in inhibiting TSH activation of thyroidal adenylate cYclase. Goal (5) will explore the possible occurrence of a TSH-sensitive membrane bound NAD(P)H oxidase in thyroid and will utilize spectrophotometric and enzymatic identifications of possible intermediates such as superoxide anion and hydroxyl radical.